Lana Del Rey was supposed to perform on 'Late Show With David Letterman' last night, but she canceled at the last minute. So the late-night host called up his pal Elvis Costello, who not only showed up to play a song, he played a brand new one.

The song, 'The Last Year of My Youth,' was reportedly written just the night before. You can watch Costello's performance of the song -- just him and his electric guitar looking back on days gone by -- above.

In a couple weeks, Costello will headline two shows at Carnegie Hall -- unbelievably, his first-ever performances at the historic venue. It's part of a new solo tour, in which the singer-songwriter will specifically construct new set lists every night to fit his mood and the city.

The tour is also called 'The Last Year of My Youth,' so you have to wonder if Costello indeed wrote the song just the other night. Either way, it's a pretty good song, and it sounds like it will appropriately reflect the tone of the upcoming shows.

And here's a clip of Costello performing the classic '(What's So Funny 'Bout) Peace, Love, and Understanding' when he guest hosted for Letterman back in 2003, when an eye infection sidelined the host: